typing: add type hints to global variables in mercurial/pycompat.py

The way `osaltsep` and `sysexecutable` were defined, pytype determined them to
be `Union[bytes, str]`.  This was a problem because that cascaded to all of the
callers, and also because it couldn't be annotated as bytes on the initial
assignment.  Therefore, we use a ternary operator.

The documentation says that `sys.executable` can either be None or an empty
string if the value couldn't be determined.  We opt for an empty string here
because there are places that blindly pass it to `os.path.xxx()` functions,
which crash if given None.  Other places test `if pycompat.sysexecutable`, so
empty string works for both.

mercurial/pycompat.py

@@ -1,425 +1,426 b''
 # pycompat.py - portability shim for python 3
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 """Mercurial portability shim for python 3.
 
 This contains aliases to hide python version-specific details from the core.
 """
 
 
 import builtins
 import codecs
 import concurrent.futures as futures
 import functools
 import getopt
 import http.client as httplib
 import http.cookiejar as cookielib
 import inspect
 import io
 import json
 import os
 import queue
 import shlex
 import socketserver
 import struct
 import sys
 import tempfile
 import xmlrpc.client as xmlrpclib
 
+from typing import (
+    List,
+    Optional,
+)
 
 ispy3 = sys.version_info[0] >= 3
 ispypy = '__pypy__' in sys.builtin_module_names
 TYPE_CHECKING = False
 
 if not globals():  # hide this from non-pytype users
     import typing
 
     TYPE_CHECKING = typing.TYPE_CHECKING
 
 
 def future_set_exception_info(f, exc_info):
     f.set_exception(exc_info[0])
 
 
 FileNotFoundError = builtins.FileNotFoundError
 
 
 def identity(a):
     return a
 
 
 def _rapply(f, xs):
     if xs is None:
         # assume None means non-value of optional data
         return xs
     if isinstance(xs, (list, set, tuple)):
         return type(xs)(_rapply(f, x) for x in xs)
     if isinstance(xs, dict):
         return type(xs)((_rapply(f, k), _rapply(f, v)) for k, v in xs.items())
     return f(xs)
 
 
 def rapply(f, xs):
     """Apply function recursively to every item preserving the data structure
 
     >>> def f(x):
     ...     return 'f(%s)' % x
     >>> rapply(f, None) is None
     True
     >>> rapply(f, 'a')
     'f(a)'
     >>> rapply(f, {'a'}) == {'f(a)'}
     True
     >>> rapply(f, ['a', 'b', None, {'c': 'd'}, []])
     ['f(a)', 'f(b)', None, {'f(c)': 'f(d)'}, []]
 
     >>> xs = [object()]
     >>> rapply(identity, xs) is xs
     True
     """
     if f is identity:
         # fast path mainly for py2
         return xs
     return _rapply(f, xs)
 
 
 if os.name == r'nt':
     # MBCS (or ANSI) filesystem encoding must be used as before.
     # Otherwise non-ASCII filenames in existing repositories would be
     # corrupted.
     # This must be set once prior to any fsencode/fsdecode calls.
     sys._enablelegacywindowsfsencoding()  # pytype: disable=module-attr
 
 fsencode = os.fsencode
 fsdecode = os.fsdecode
-oscurdir = os.curdir.encode('ascii')
-oslinesep = os.linesep.encode('ascii')
-osname = os.name.encode('ascii')
-ospathsep = os.pathsep.encode('ascii')
-ospardir = os.pardir.encode('ascii')
-ossep = os.sep.encode('ascii')
-osaltsep = os.altsep
-if osaltsep:
-    osaltsep = osaltsep.encode('ascii')
-osdevnull = os.devnull.encode('ascii')
+oscurdir: bytes = os.curdir.encode('ascii')
+oslinesep: bytes = os.linesep.encode('ascii')
+osname: bytes = os.name.encode('ascii')
+ospathsep: bytes = os.pathsep.encode('ascii')
+ospardir: bytes = os.pardir.encode('ascii')
+ossep: bytes = os.sep.encode('ascii')
+osaltsep: Optional[bytes] = os.altsep.encode('ascii') if os.altsep else None
+osdevnull: bytes = os.devnull.encode('ascii')
 
-sysplatform = sys.platform.encode('ascii')
-sysexecutable = sys.executable
-if sysexecutable:
-    sysexecutable = os.fsencode(sysexecutable)
+sysplatform: bytes = sys.platform.encode('ascii')
+sysexecutable: bytes = os.fsencode(sys.executable) if sys.executable else b''
 
 
 def maplist(*args):
     return list(map(*args))
 
 
 def rangelist(*args):
     return list(range(*args))
 
 
 def ziplist(*args):
     return list(zip(*args))
 
 
 rawinput = input
 getargspec = inspect.getfullargspec
 
 long = int
 
 if getattr(sys, 'argv', None) is not None:
     # On POSIX, the char** argv array is converted to Python str using
     # Py_DecodeLocale(). The inverse of this is Py_EncodeLocale(), which
     # isn't directly callable from Python code. In practice, os.fsencode()
     # can be used instead (this is recommended by Python's documentation
     # for sys.argv).
     #
     # On Windows, the wchar_t **argv is passed into the interpreter as-is.
     # Like POSIX, we need to emulate what Py_EncodeLocale() would do. But
     # there's an additional wrinkle. What we really want to access is the
     # ANSI codepage representation of the arguments, as this is what
     # `int main()` would receive if Python 3 didn't define `int wmain()`
     # (this is how Python 2 worked). To get that, we encode with the mbcs
     # encoding, which will pass CP_ACP to the underlying Windows API to
     # produce bytes.
+    sysargv: List[bytes] = []
     if os.name == r'nt':
         sysargv = [a.encode("mbcs", "ignore") for a in sys.argv]
     else:
         sysargv = [fsencode(a) for a in sys.argv]
 
 bytechr = struct.Struct('>B').pack
 byterepr = b'%r'.__mod__
 
 
 class bytestr(bytes):
     """A bytes which mostly acts as a Python 2 str
 
     >>> bytestr(), bytestr(bytearray(b'foo')), bytestr(u'ascii'), bytestr(1)
     ('', 'foo', 'ascii', '1')
     >>> s = bytestr(b'foo')
     >>> assert s is bytestr(s)
 
     __bytes__() should be called if provided:
 
     >>> class bytesable:
     ...     def __bytes__(self):
     ...         return b'bytes'
     >>> bytestr(bytesable())
     'bytes'
 
     There's no implicit conversion from non-ascii str as its encoding is
     unknown:
 
     >>> bytestr(chr(0x80)) # doctest: +ELLIPSIS
     Traceback (most recent call last):
       ...
     UnicodeEncodeError: ...
 
     Comparison between bytestr and bytes should work:
 
     >>> assert bytestr(b'foo') == b'foo'
     >>> assert b'foo' == bytestr(b'foo')
     >>> assert b'f' in bytestr(b'foo')
     >>> assert bytestr(b'f') in b'foo'
 
     Sliced elements should be bytes, not integer:
 
     >>> s[1], s[:2]
     (b'o', b'fo')
     >>> list(s), list(reversed(s))
     ([b'f', b'o', b'o'], [b'o', b'o', b'f'])
 
     As bytestr type isn't propagated across operations, you need to cast
     bytes to bytestr explicitly:
 
     >>> s = bytestr(b'foo').upper()
     >>> t = bytestr(s)
     >>> s[0], t[0]
     (70, b'F')
 
     Be careful to not pass a bytestr object to a function which expects
     bytearray-like behavior.
 
     >>> t = bytes(t)  # cast to bytes
     >>> assert type(t) is bytes
     """
 
     # Trick pytype into not demanding Iterable[int] be passed to __new__(),
     # since the appropriate bytes format is done internally.
     #
     # https://github.com/google/pytype/issues/500
     if TYPE_CHECKING:
 
         def __init__(self, s=b''):
             pass
 
     def __new__(cls, s=b''):
         if isinstance(s, bytestr):
             return s
         if not isinstance(
             s, (bytes, bytearray)
         ) and not hasattr(  # hasattr-py3-only
             s, u'__bytes__'
         ):
             s = str(s).encode('ascii')
         return bytes.__new__(cls, s)
 
     def __getitem__(self, key):
         s = bytes.__getitem__(self, key)
         if not isinstance(s, bytes):
             s = bytechr(s)
         return s
 
     def __iter__(self):
         return iterbytestr(bytes.__iter__(self))
 
     def __repr__(self):
         return bytes.__repr__(self)[1:]  # drop b''
 
 
 def iterbytestr(s):
     """Iterate bytes as if it were a str object of Python 2"""
     return map(bytechr, s)
 
 
 def maybebytestr(s):
     """Promote bytes to bytestr"""
     if isinstance(s, bytes):
         return bytestr(s)
     return s
 
 
 def sysbytes(s):
     """Convert an internal str (e.g. keyword, __doc__) back to bytes
 
     This never raises UnicodeEncodeError, but only ASCII characters
     can be round-trip by sysstr(sysbytes(s)).
     """
     if isinstance(s, bytes):
         return s
     return s.encode('utf-8')
 
 
 def sysstr(s):
     """Return a keyword str to be passed to Python functions such as
     getattr() and str.encode()
 
     This never raises UnicodeDecodeError. Non-ascii characters are
     considered invalid and mapped to arbitrary but unique code points
     such that 'sysstr(a) != sysstr(b)' for all 'a != b'.
     """
     if isinstance(s, builtins.str):
         return s
     return s.decode('latin-1')
 
 
 def strurl(url):
     """Converts a bytes url back to str"""
     if isinstance(url, bytes):
         return url.decode('ascii')
     return url
 
 
 def bytesurl(url):
     """Converts a str url to bytes by encoding in ascii"""
     if isinstance(url, str):
         return url.encode('ascii')
     return url
 
 
 def raisewithtb(exc, tb):
     """Raise exception with the given traceback"""
     raise exc.with_traceback(tb)
 
 
 def getdoc(obj):
     """Get docstring as bytes; may be None so gettext() won't confuse it
     with _('')"""
     doc = getattr(obj, '__doc__', None)
     if doc is None:
         return doc
     return sysbytes(doc)
 
 
 def _wrapattrfunc(f):
     @functools.wraps(f)
     def w(object, name, *args):
         return f(object, sysstr(name), *args)
 
     return w
 
 
 # these wrappers are automagically imported by hgloader
 delattr = _wrapattrfunc(builtins.delattr)
 getattr = _wrapattrfunc(builtins.getattr)
 hasattr = _wrapattrfunc(builtins.hasattr)
 setattr = _wrapattrfunc(builtins.setattr)
 xrange = builtins.range
 unicode = str
 
 
 def open(name, mode=b'r', buffering=-1, encoding=None):
     return builtins.open(name, sysstr(mode), buffering, encoding)
 
 
 safehasattr = _wrapattrfunc(builtins.hasattr)
 
 
 def _getoptbwrapper(orig, args, shortlist, namelist):
     """
     Takes bytes arguments, converts them to unicode, pass them to
     getopt.getopt(), convert the returned values back to bytes and then
     return them for Python 3 compatibility as getopt.getopt() don't accepts
     bytes on Python 3.
     """
     args = [a.decode('latin-1') for a in args]
     shortlist = shortlist.decode('latin-1')
     namelist = [a.decode('latin-1') for a in namelist]
     opts, args = orig(args, shortlist, namelist)
     opts = [(a[0].encode('latin-1'), a[1].encode('latin-1')) for a in opts]
     args = [a.encode('latin-1') for a in args]
     return opts, args
 
 
 def strkwargs(dic):
     """
     Converts the keys of a python dictonary to str i.e. unicodes so that
     they can be passed as keyword arguments as dictionaries with bytes keys
     can't be passed as keyword arguments to functions on Python 3.
     """
     dic = {k.decode('latin-1'): v for k, v in dic.items()}
     return dic
 
 
 def byteskwargs(dic):
     """
     Converts keys of python dictionaries to bytes as they were converted to
     str to pass that dictonary as a keyword argument on Python 3.
     """
     dic = {k.encode('latin-1'): v for k, v in dic.items()}
     return dic
 
 
 # TODO: handle shlex.shlex().
 def shlexsplit(s, comments=False, posix=True):
     """
     Takes bytes argument, convert it to str i.e. unicodes, pass that into
     shlex.split(), convert the returned value to bytes and return that for
     Python 3 compatibility as shelx.split() don't accept bytes on Python 3.
     """
     ret = shlex.split(s.decode('latin-1'), comments, posix)
     return [a.encode('latin-1') for a in ret]
 
 
 iteritems = lambda x: x.items()
 itervalues = lambda x: x.values()
 
 json_loads = json.loads
 
-isjython = sysplatform.startswith(b'java')
+isjython: bool = sysplatform.startswith(b'java')
 
-isdarwin = sysplatform.startswith(b'darwin')
-islinux = sysplatform.startswith(b'linux')
-isposix = osname == b'posix'
-iswindows = osname == b'nt'
+isdarwin: bool = sysplatform.startswith(b'darwin')
+islinux: bool = sysplatform.startswith(b'linux')
+isposix: bool = osname == b'posix'
+iswindows: bool = osname == b'nt'
 
 
 def getoptb(args, shortlist, namelist):
     return _getoptbwrapper(getopt.getopt, args, shortlist, namelist)
 
 
 def gnugetoptb(args, shortlist, namelist):
     return _getoptbwrapper(getopt.gnu_getopt, args, shortlist, namelist)
 
 
 def mkdtemp(suffix=b'', prefix=b'tmp', dir=None):
     return tempfile.mkdtemp(suffix, prefix, dir)
 
 
 # text=True is not supported; use util.from/tonativeeol() instead
 def mkstemp(suffix=b'', prefix=b'tmp', dir=None):
     return tempfile.mkstemp(suffix, prefix, dir)
 
 
 # TemporaryFile does not support an "encoding=" argument on python2.
 # This wrapper file are always open in byte mode.
 def unnamedtempfile(mode=None, *args, **kwargs):
     if mode is None:
         mode = 'w+b'
     else:
         mode = sysstr(mode)
     assert 'b' in mode
     return tempfile.TemporaryFile(mode, *args, **kwargs)
 
 
 # NamedTemporaryFile does not support an "encoding=" argument on python2.
 # This wrapper file are always open in byte mode.
 def namedtempfile(
     mode=b'w+b', bufsize=-1, suffix=b'', prefix=b'tmp', dir=None, delete=True
 ):
     mode = sysstr(mode)
     assert 'b' in mode
     return tempfile.NamedTemporaryFile(
         mode, bufsize, suffix=suffix, prefix=prefix, dir=dir, delete=delete
     )